1. Field of the Invention
The present invention is directed to a rotatable anode for an X-ray tube which is composed of a porous body of a difficult to melt material enclosed in a sealed fashion within an enveloping layer of difficult to melt material.
2. Prior Art
A rotatable anode for an X-ray tube which are frequently known and frequently employed are composed of a difficult to melt or fuse material and are, in addition, coated on the surface on which the electrons hit or impinge with a difficult to melt material having a high atomic number. An example of such an anode which has a porous body of a difficult to fuse material and is sealed within an enveloping cover is disclosed in U.S. Pat. No. 3,969,131.
Since, in the production of X-rays, all of the applied electrical energy except for approximately 1% is converted into heat, the structure must provide for a good dissipation or transport of the heat. A possibility of promoting the dissipation or transportation of the heat is accomplished by rotation of a known rotatable anode. In a rotatable anode, the electron beam is directed at a portion or segment of an annular surface which, due to the rotation of the anode, causes the surface on which the electron beam has been hitting to be moved out of the path of the electrons. While being conveyed away from the path of the electrons, the surface is able to emit heat to the surroundings by either radiation or thermal conduction. For this reason, the specific stress capacities or load carrying capacities of the X-ray tube with a rotatable anode is greater than in a tube which has a fixed or stationary anode.
In the case of anodes in accordance with the above-identified U.S. Pat. No. 3,969,131, the anode body is composed of a multi-layer construction with an isotropic graphite body which is provided with a coating adhering on its surfaces and sealing the latter. However, this constructive solution for adapting or adjusting the expansion coefficients, which solution is employed for the purpose of obtaining a thermally stable body, has not been capable of being introduced into X-ray technology because the heat transmission from the metal ring or coating into the multi-layer graphite section or body is insufficient.